Refrigerant Safety

The excerpt below is from "Refrigerant Safety," originally
printed in the
ASHRAE Journal (July
1994, pp. 17-26). It is presented by permission of the author
and the ASHRAE Journal.

"The alternative refrigerants are as safe or
safer than those they replace, but more care is needed with
all refrigerants."

Dictionaries define safety as being free from harm or the
risk of injury or loss. The concerns usually associated with
refrigerants are toxicity, flammability, and physical
hazards. Are refrigerants completely safe? No, all pose one
or more of these concerns. But can refrigerants, and
especially the new refrigerants, be used safely? Yes, and
generally more so than in the past.

Refrigerant History

The first practical refrigerating machine was built by
Jacob Perkins in 1834; it used ether in a vapor-compression
cycle. The first absorption machine was developed by Edmond
Carr, in 1850, using water and sulfuric acid. His brother,
Ferdinand Carr, demonstrated an ammonia/water refrigeration
machine in 1859. A mixture called chemogene, consisting of
petrol ether and naphtha, was patented as a refrigerant for
vapor-compression systems in 1866. Carbon dioxide was
introduced as a refrigerant in the same year. Ammonia was
first used in vapor-compression systems in 1873, sulfur
dioxide and methyl ether in 1875, and methyl chloride in
1878. Dichloroethene (dilene) was used in Willis Carrier's
first centrifugal compressors, and was replaced with
methylene chloride in 1926.

Nearly all of the early refrigerants were flammable,
toxic, or both, and some also were highly reactive. Accidents
were common. The task of finding a nonflammable refrigerant
with good stability was given to Thomas Midgley in 1926. He
already had established himself by finding tetraethyl lead,
to improve the octane rating of gasoline.

With his associates Henne and McNary, Midgley observed
that the refrigerants then in use comprised relatively few
chemical elements, clustered in an intersecting row and
column of the periodic table of elements. The element at the
intersection was fluorine, known to be toxic by itself.
Midgley and his collaborators felt, however, that compounds
containing it should be both nontoxic and nonflammable.

Their attention was drawn to organic fluorides by an error
in the literature. It showed the boiling point for
tetrafluoromethane (carbon tetrafluoride) to be high compared
to those for other fluorinated compounds. The correct boiling
temperature later was found to be much lower. Nevertheless,
the incorrect value was in the range sought and led to
evaluation of organic fluorides as candidates. The shorthand
convention, later introduced to simplify identification of
the organic fluorides for a systematic search, is used today
as the numbering system for refrigerants. The number
designations unambiguously indicate both the chemical
compositions and structures.

Within three days of starting, Midgley and his
collaborators had identified and synthesized
dichlorodifluoromethane, now known as R-12.

The first toxicity test was performed by exposing a guinea
pig to the new compound. Surprisingly, the animal was
completely unaffected, but the guinea pig died when the test
was repeated with another sample. Subsequent examination of
the antimony trifluoride, used to prepare the
dichlorodifluoromethane from carbon tetrachloride, showed
that four of the five bottles available at the time contained
water. This contaminant forms phosgene (COCl2) during the
reaction of antimony trifluoride with carbon tetrachloride.
Had the initial test used one of the other samples, the
discovery of organic fluoride refrigerants might well have
been delayed for years.

The development of fluorocarbon refrigerants was announced
in April 1930. To demonstrate the safety of the new
compounds, at a meeting of the American Chemical Society, Dr.
Midgley inhaled R-12 and blew out a candle with it. While
this demonstration was dramatic, it would be a clear
violation of safe handling practices today.

CFC Refrigerants

Commercial chlorofluorocarbon (CFC) production began with
R-12 in early 1931, R-11 in 1932, R-114 in 1933, and R-113 in
1934; the first hydrochlorofluorocarbon (HCFC) refrigerant,
R-22, was produced in 1936. By 1963, these five products
accounted for 98% of the total production of the organic
fluorine industry. Annual sales had reached 372 million
pounds, half of it R-12. These chlorofluorochemicals were
viewed as nearly nontoxic, nonflammable, and highly stable in
addition to offering good thermodynamic properties and
materials compatibility at low cost. Close to half a century
passed between the introduction of CFCs and recognition of
their harm to the environment when released. Specific
concerns relate to their depletion of stratospheric ozone and
to possible global warming by actions as greenhouse gases.
Ironically, the high stability of CFCs enables them to
deliver ozone-depleting chlorine to the stratosphere. The
same stability prolongs their atmospheric lifetimes, and thus
their persistence as greenhouse gases.

"Ideal" Refrigerants

In addition to having the desired thermodynamic
properties, an ideal refrigerant would be nontoxic,
nonflammable, completely stable inside a system,
environmentally benign even with respect to decomposition
products, and abundantly available or easy to manufacture. It
also would be self-lubricating (or at least compatible with
lubricants), compatible with other materials used to
fabricate and service refrigeration systems, easy to handle
and detect, and low in cost. It would not require extreme
pressures, either high or low. There are additional criteria,
but no current refrigerants are ideal even based on the
partial list. Furthermore, no ideal refrigerants are likely
to be discovered in the future.

Toxicity

A fundamental tenet of toxicology, attributed to
Paracelsus in the 16th century, is "dosis solo facit
venenum", the dose makes the poison. All substances are
poisons in sufficient amounts. Toxic effects have been
observed for such common substances as water, table salt,
oxygen, and carbon dioxide in extreme quantities. The
difference between those regarded as safe and those viewed as
toxic is the quantity or concentration needed to cause harm
and, in some cases, the duration or repetition of exposures.
Substances that pose high risks with small quantities, even
with short exposures, are regarded as highly toxic. Those for
which practical exposures cause no harm are viewed as
safer.

There are multiple reasons that toxicity concerns have
surfaced with the introduction of new refrigerants. First,
they are less familiar. Second, public consciousness of
health hazards is growing. Manufacturer concerns with
liability also have increased. Third, few refrigerant users
fully understand the measures and terminology used to report
the extensive toxicity data being gathered. And fourth, the
new chemicals are somewhat less stable when released and
exposed to air, water vapor, other atmospheric chemicals, and
sunlight. This increased reactivity is desired to reduce
atmospheric longevity, and thereby to reduce the fraction of
emissions that reaches the stratospheric ozone layer or that
persists in the atmosphere as a greenhouse gas. While
toxicity often increases with higher reactivity, atmospheric
reactivity is not necessarily pertinent. The most toxic
compounds are those with sufficient stability to enter the
body and then decompose or destructively metabolize in a
critical organ. As examples, most CFCs are very stable in the
atmosphere, generally less stable than either HCFCs or
hydrofluorocarbons (HFCs) in refrigeration systems, and
generally have comparable or greater acute toxicity than
HCFCs or HFCs.

Concerns with refrigerant safety have been heightened by
negative marketing by competing equipment vendors. Frequent
overstatement, to influence customer perceptions, coupled
with contradictions have fueled discomfort in refrigerant
choices for all of the alternative refrigerants.

Acute versus Chronic Risks

Acute toxicity refers to the impacts of single exposures,
often at high concentrations. It suggests the possible risk
levels for the consequences of accidental releases, such as
from a spill or rupture. It also is a gauge for service
operations in which high exposures may be experienced for
brief periods, such as upon opening a compressor or removing
a gasket that may have refrigerant trapped under it.

Chronic toxicity refers to the effects of repeated or
sustained exposures over a long period, such as that
experienced in a lifetime of working in machinery rooms. Few
technicians actually spend their full day in machinery rooms
and concentrations may fluctuate. Most chronic exposure
indices, therefore, are expressed as time-weighted average
(TWA) values.

The nature of chronic effects is such that most can be
anticipated and/or monitored, and occupational safety
measures can be taken to minimize their impacts. As an
example, refriger- ant concentrations can be lowered by
designing equipment with reduced leakage and promptly
repairing leaks that do occur. Refrigerant sensors can be
used to sense and warn technicians of concentration
increases. Further measures are identified below, in the
discussion of safety standards.

From a safety perspective, the goal is to reduce both
acute and chronic risks.

PAFT Tests

The Programme for Alternative Fluorocarbon Toxicity
Testing (PAFT) is a cooperative effort sponsored by the major
producers of CFCs from nine countries. PAFT was designed to
accelerate the development of toxicology data for
fluorocarbon substitutes, as refrigerants and for other
purposes. Examples of the other uses include as blowing
agents, aerosol propellants, and solvents. The PAFT research
entails more than 100 individual toxicology tests by more
than a dozen laboratories in Europe, Japan, and the United
States. The first tests were launched in 1987, to address
R-123 and R-134a (PAFT I). Subsequent programs were initiated
for R-141b (PAFT II), R-124 and R-125 (PAFT III), R-225ca and
R-225cb (PAFT IV), and R-32 (PAFT V). The cost of testing for
each compound is $1-5 million and the duration is 2-6 years,
depending on the specific tests deemed necessary or indicated
by initial findings.

These PAFT studies investigate acute toxicity (short-term
exposures to high concentrations, such as from accidental
releases), subchronic toxicity (repeated exposure to
determine any overall toxicological effect), and chronic
toxicity and carcinogicity (lifetime testing to assess
late-in-life toxicity or potential to cause cancer). The
experiments also gauge genotoxicity (effects on genetic
material, an early screen for possible cancer-inducing
activity), reproductive and developmental toxicity
(teratology, assessment of the effects on the reproductive
system and of the potential for causing birth defects), and
ecotoxicity (assessment of potential to affect living
organisms in the environment).

A new program, initiated in 1994, is addressing the
mechanistic causes of tumors and other effects observed in
other programs. PAFT M was spurred by findings of benign
tumors in earlier tests of R-123, R-134a, and R-141b.
Although the tumors occurred late in life and were neither
cancerous nor life threatening, a better understanding of
causal effects is being sought.

Table 1 explains key toxicity and safety terminology to
assist readers in understanding the following summaries.

R-123 Toxicology

Tests of R-123 indicate that it has very low acute
inhalation toxicity, as measured by the concentration that
causes 50% mortality in experimental animals, a 4-hour LC50
of 32,000 ppm in rats. A cardiac sensitization response was
observed at approximately 20,000 ppm. This response was
measured in experimental screening with dogs, with
simultaneous injection of epinephrine to simulate human
stress reactions. Anesthetic-like effects (e.g., weakness,
disorientation, or incoordination) were observed at
concentrations greater than 5,000 ppm, or 0.5%. R-123 has
very low dermal toxicity (by skin application) and is only a
mild eye irritant. Long-term inhalation caused an increase in
the incidence of benign tumors in the liver, pancreas, and
testis of rats. None of the tumors attributable to the
exposures were malignant or life-threatening; all occurred
near the end of the study, late in the lives of the test
specimens. The exposed animals actually exhibited higher
survival rates at the end of testing than those in the
control group. The rats exposed to higher concentrations also
experienced slight reductions in body weight and decreases in
cholesterol and triglyceride levels. Studies are continuing
to investigate the biological relevance of the tumors to
humans. The tests completed to date indicate that R-123 is
neither a developmental toxicant nor a genotoxin.

Based on the findings of extensive testing, R-123 has been
deemed to have low toxicity. Refrigerant manufacturers
recommend that long-term, occupational exposures not exceed
limits of 10 and 30 ppm, on eight-hour time-weighted average
(TWA) bases. One manufacturer suggests a limit of 100 ppm,
also TWA, but is expected to revise this recommendation to
somewhere in the 10-30 ppm range. The differences in
recommended limits stem from conservative interpretation of
the data. As discussed below, occupational exposures can be
held well below even the most stringent of these
recommendations.

The exposure limits are based on chronic toxicity concerns
and are below those at which toxic effects were observed in
the laboratory tests. Higher concentrations are allowable for
short-periods, but exposures still should be kept to the
minimum practicable, as for all chemicals.

Table 1 A Glossary of Safety Terminology

acute toxicity

the effect of a single, short term exposure, as might
occur during an accidental release

Ames assay

a test for mutagenicity on bacteria, designed as a
screen for possible carcinogens

benign

not malignant; not likely to cause death or
deterioration

carcinogen

a substance that causes cancer

cardiac sensitization

an effect in which the heart is rendered more sensitive
to the action of adrenalin and similar drugs, possibly
resulting in cardiac arrythmia and arrest (heart
attack)

Ceiling

an exposure level (as in PEL-C, REL-C, or TLV-C) that
should not be exceeded during any part of the day, assessed
as a 15-minute TWA unless otherwise specified

effects on genetic material, an early screen for
possible cancer-inducing activity

IDLH

Immediately Dangerous to Life and Health (set by the
U.S. National Institute of Occupational Safety and Health,
NIOSH), the maximum concentration of airborne contaminants,
normally expressed as parts per million (ppm), from which
one could escape within 30 minutes without a respirator and
without experi- encing any escape impairing (e.g., severe
eye irritation) or irre- versible health effects

Lower Flammability Limit, the minimum concentration in
air at which flame propagation occurs

mouse micronucleus assay

a test for changes in chromosomes in a mouse, designed
as a screen for possible mutagens and carcinogens

NOEL

No Observed Effect Level, the maximum dose at which no
signs of harm are observed

mutagen

a substance that causes a change in the amount or
structure of genetic material

PAFT

Programme for Alternative Fluorocarbon Toxicity Testing
a cooperative effort to accelerate the development of
toxicology data for fluorocarbon substitutes

PEL

Permissible Exposure Levels (set by the U.S.
Occupational Safety and Health Administration, OSHA), A PEL
is the TWA concentration that must not be exceeded during
any eight-hour work shift of a 40-hour work week. Chemical
manufacturers pub- lish similar recommendations (e.g.,
acceptable exposure level, AEL; industrial exposure limit,
IEL; or occupational exposure limit, OEL depending on
company), generally for substances for which a PEL has not
been established.

ppm

parts per million (generally in air at 25 °C, 77
°F, and 1 atmo- sphere of pressure, 14.7 psia), may be
converted to percentages by dividing by 10,000

REL

Recommended Exposure Limit (set by NIOSH), a
recommended occupational exposure limit generally on a TWA
basis for up to ten hour/day during a 40 hour work week;
may also be on a STEL or Ceiling basis

STEL

Short-Term Exposure Limit

subchronic toxicity

the effects obtained after repeated exposures to a
chemical, usually for 90 days

TLV

Threshold Limit Value (set by the American Conference
of Gov- ernment Industrial Hygienists, ACGIH), the airborne
concentration of a substance to which nearly all workers
may be exposed without adverse health effects

TWA

Time-Weighted Average for concentrations

UFL

Upper Flammability Limit, the maximum concentration in
air at which flame propagation occurs

R-134a Toxicology

R-134a also has very low acute inhalation toxicity. The
lowest concentration that causes mortality in rats, the
4-hour Approximate Lethal Concentration (ALC), exceeds
500,000 ppm. The cardiac sensitization response level for
R-134a is approximately 75,000 ppm. Anesthetic-like effects
are observed at concentrations greater than 200,000 ppm, or
20%. Long term exposures with very high concentrations,
50,000 ppm, caused an increased incidence of benign tumors in
the testis of rats. Again, none of the observed tumors were
life-threatening, and all occurred near the end of the study.
The evidence from all tests in cultured cells or organisms,
as well as in laboratory animals, indicates that R-134a in
not genotoxic and that the increased incidence in benign
tumors is not due to an effect on genetic material.

The test findings indicate that R-134a has very low acute
and subchronic inhalation toxicity, is not a developmental
toxicant, and is not genotoxic. Most refrigerant
manufacturers recommend that TWA occupational exposures not
exceed 1,000 ppm; this also is the level recommended by the
American Industrial Hygiene Association, Workplace
Environmental Exposure Limit (WEEL) Committee. Again,
exposures still should be kept to the practicable
minimum.

It is important to note that the tumors attributable to
the R-123 and R-134a exposures were not cancerous. The
findings reflect an increase in tumor incidence compared to
rats in the experimental control group, those not exposed to
the refrigerants. Some tumors also were observed in this
control group, but not as many. Also, the recommended
occupational exposure limit for each refrigerant is below the
level at which toxic effects were observed in laboratory
animals. The use of rats, dogs, and other animals is based on
accepted scientific procedures and sensi- tivities to
specific concerns by species. The lower exposure limit
affords both a margin of safety and a conservative reflec-
tion of potential differences, between responses in
individual humans and between humans and test animals.

Other Refrigerants

Information on the toxicity of other refrigerants is
available from chemical manufacturers, published literature,
and chemical and safety databases. The toxicology findings
for other refrigerants covered by PAFT also are available in
reference . R-123 and R-134a were summarized here as the
newest of the widely used refrigerants for chillers. Other
chiller refrigerants are addressed in less detail below, and
a survey of toxicity data is underway, by the author, on
alternative refrigerants for additional applications.

Relative Impacts

Table 2 summarizes safety data, including acute,
subchronic, and chronic toxicity indicators, for the
refrigerants most commonly used in chillers. It also presents
the lower and upper flammability limits (LFL and UFL) of
refrigerants in air, calculated heats of combustion, and the
safety classifications assigned by ASHRAE Standard 34. The
table enables comparison of data for the alternative
refrigerants with corresponding information for R-11 and
R-12, which are being phased out to protect the environment.
Safety specialists, including toxicologists, industrial
hygienists, and fire prevention authorities, should be
consulted for interpretations, since other data and specific
conditions may be pertinent for individual applications.
Also, chemical manufacturers provide frequently updated
Material Safety Data Sheets (MSDSs) that summarize risks,
recommend first aid measures, and give other safety guidance.
Individuals who work with refrigerants should be familiar
with these documents and have access to them for reference.
R-11 and R-12 have been in wide use for more than sixty
years. While some accidents have occurred with them, both are
regarded as fairly safe substances. Both have been used as
aerosol propellants for consumer products, including
cosmetics likely to be inhaled or sprayed on exposed skin.
Both are used as propellants in metered dose inhalers,
intended for inhalation with medications. As indicated in the
table, and further discussed below, the alternative
refrigerants introduced toa replace R-11 and R-12 are safer
in many respects, especially those involving acute toxicity
concerns.

Table 2. Safety Indicators for
Common Chiller Refrigerants

R-11

R-123

R-12

R-134a

R-22

R-717

Acute (short term)
toxicity
LC50, 4 hr rat (ppm)

26,200

32,000

760,000

>500,000

220,000

2,000
b

Cardiac sensitization,
dog (ppm)

5,000
c

20,000

50,000

75,000

50,000

5,000

Anesthetic effect
(ppm)

10,000

5,000

>200,000

>200,000

200,000

500

NIOSH IDLH (ppm)

10,000
d

4,000
e

50,000

50,000
e

50,000
e

500

Short-term exposure
limit (ppm)

1,000

1,000
f

50,000

75,000

50,000

35

Subchronic toxicity
NOEL, rat (ppm)

10,000

1,000

10,000

50,000

10,000

50

Mutagenicity or
Carcinogicity

Ames assay

negative

negative

negative

negative

negative

unknown

Mouse micronucleus
assay

negative

negative

negative

negative

negative

g

Carcinogenic

no

no
h

no

no
h

weakly
i

unknown

Teratogenicity
rats or rabbits

none

none

none

none

none

unknown

Chronic (long term)
toxicity

Occupational exposure
limit (ppm)

C1000 (PEL, TLV-C)

10-30 (manufacturer)

1,000 (PEL, TLV-TWA)

1,000 (manufacturer)

1,000 (PEL, TLV-TWA)

50 (PEL
j/sup>)

Flammability

LFL-UFL (%vol in
air)

none
k

none
k

none
k

none
k

none
k

15-25
l

Heat of combustion
(MJ/kg)

0.9

2.1

-0.8

4.2

2.2

22.5

Safety classification
m

A1

B1

A1

A1

A1

B2

The alternative refrigerants are as safe or safer than
those they replace, but more care is needed with all
refrigerants.

Dictionaries define "safety" as "being free from harm or
the risk of injury or loss." The concerns usually associated
with refrigerants are toxicity, flammability, and physical
hazards. Are refrigerants completely safe? No, all pose one
or more of these concerns. But can refrigerants, and
especially the new refrigerants, be used safely? Yes, and
generally more so than in the past.

The article
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